Are Vajrayana and Tibetan Buddhism the same thing?

This is a hugely amateurish question, for which I apologize, but: are Vajrayana and Tibetan Buddhism the same thing? If not, how are they related? In particular, does the term "Tibetan Buddhism" refer to a specific school of Buddhist thought and practice, or does it just generically refer to any sort of Buddhism that is practiced in Tibet? Wikipedia treats the two as separate entities, but some other sources (e.g. this ) treat them as effectively the same.